Gas turbine apparatus and a starting method thereof

ABSTRACT

A gas turbine starting method, comprising the steps of rotatively driving a turbine by a motor coupled to the turbine, while at the same time supplying a compressed air to a combustor by an air compressor operating in interlocking motion with the turbine, starting a fuel supply to the combustor when a revolution speed of the turbine has reached up to a predetermined value, and simultaneously starting an igniting operation on an air-fuel mixture in the combustor, wherein at least during the igniting operation to the air-fuel mixture in the combustor, a quantity of fuel supply per unit time to the combustor is increased while increasing the revolution speed of the turbine, to thereby ensuring the ignition of the air-fuel mixture under various conditions, and depressing the temperature rise of the gas turbine, which may otherwise occur immediately after the ignition.

FIELD OF THE INVENTION

The present invention relates to a gas turbine apparatus and a startingmethod thereof, and in particular, to a starting method for starting agas turbine apparatus by using a starting motor.

BACKGROUND OF THE INVENTION

In general, a gas turbine apparatus basically comprises a turbinemounted on a rotary shaft, a combustor for burning a mixture of fuel andair to generate a combustion gas, a fuel flow control valve forcontrolling a quantity of fuel supply to the combustor, an aircompressor for supplying the combustor with compressed air, the aircompressor operating in interlocking motion with the turbine, and so on.In thus constructed apparatus, the air-fuel mixture produced by means ofthe fuel flow control valve and the air compressor is burnt to generatea combustion gas of high temperature and high pressure, which is thensupplied to the turbine to make it revolve at high speed.

In this type of gas turbine apparatus, when it is to be started, such amethod has been employed in which the turbine is driven by a motor forstarting to actuate the gas turbine apparatus. That is, first of all,the turbine is rotatively driven by the motor while at the same time theair compressor is driven by the motor via the rotary shaft to start asupply of the compressed air to the combustor. After that, the fuel flowcontrol valve is opened to supply the combustor with a fuel to produce amixture of compressed air and the fuel therein. Subsequently, anigniting operation for the air-fuel mixture is started in the combustor,and then the air-fuel mixture is burned to generate the combustion gas,which is supplied to the turbine thereby making the turbine revolve athigh speed.

In this regard, one of the requirements for igniting the air-fuelmixture is an appropriate mass ratio (or weight ratio) of air and fuelin the mixture, or an air fuel ratio (sometimes abbreviated to A/F). Theair fuel ratio is the mass ratio between the air and the fuel, or amixture ratio, provided for the combustion, which may be obtained as aflow rate of the air per unit time divided by a flow rate of the fuelper unit time. As described above, since the air is compressed by thecompressor and then fed to the combustor, and this compressor has beendriven in interlocking motion with the turbine, the flow rate of the aircan be calculated based on a revolution speed of the turbine. On theother hand, the flow rate of the fuel can be calculated based on anopening of the fuel flow control valve. Accordingly, the air fuel ratiocan be determined from the revolution speed of the turbine and theopening of the fuel flow control valve.

FIG. 5 is a schematic diagram of the revolution speed of the turbine,the opening of the fuel flow control valve and a temperature of anexhaust gas of the conventional turbine apparatus, each illustrated as afunction of an elapsed time during a starting operation thereof. In FIG.5, NR(Number of Revolution) represents a revolution speed of theturbine, FCV(Fuel Control Valve) represents an opening of the fuel flowcontrol valve, EGT(Exhaust Gas Temperature) represents a temperature ofthe exhaust gas, and MC(Motor Current) represents a quantity of currentsupply per unit time to the motor, respectively.

As can be seen from FIG. 5, firstly the turbine is rotatively driven bythe motor (see dotted line MC of FIG. 5), and after the revolution speedof the turbine reaches up to the revolution speed NR₁ required forignition, the motor is controlled to maintain said revolution speed NR₁.Then, the fuel supply to the combustor is begun to produce the air-fuelmixture and simultaneously the igniting operation is started (t₁). Atthis time, the quantity of fuel supply per unit time (the opening of thefuel flow control valve) is maintained, as shown in FIG. 5, to apredetermined level of fuel supply quantity (fcv₁) suitable for theignition.

Then, the air-fuel mixture is ignited to generate the combustion gas(t₂), which is fed to the turbine so as to provide the power thereto,and thereby the revolution speed of the turbine is increased.Subsequently, the rotatively driving operation of the motor is stopped.When the rotatively driving operation by the combustion gas begins, aspeed up of the turbine is put under the control by adjusting the supplyquantity of the combustion gas to the turbine. That is, a speed upcontrol is applied, in which the opening of the fuel flow control valveis operated to increase the revolution speed of the turbine so that anacceleration of revolution of the turbine may reach up to apredetermined target acceleration level.

As described above, during the igniting operation (time period from t₁to t₂), the air fuel ratio is set to be a certain value suitable forignition, and accordingly, as shown in FIG. 5, the revolution speed ofthe turbine (the flow rate of the compressed air) and the opening of thefuel flow control valve (the fuel supply quantity) are maintained to beconstant respectively. Thus, the igniting operation is performed underthe specific air fuel ratio suitable for ignition so that the air-fuelmixture may be ignited soon.

However, the air fuel ratio suitable for ignition varies depending onthe specific actual conditions in respective ignition operations. Forexample, when the temperature of surrounding environment is low, it israther difficult to accomplish a smooth ignition, while an ignition forrestarting under a high temperature condition of the gas turbine mainbody shortly after the stop of operation may be performed easily. Thatis, the ignition may not always be successfully performed under the sameair fuel ratio on every occasion, and sometimes the air-fuel mixturecannot be ignited resulting in a failure of the starting operation.

In order to deal with the problem described above, one approach has beenconventionally attempted, in which, as shown in FIG. 6, while keepingthe revolution speed of the turbine to be constant, the opening of thefuel flow control valve is increased gradually to vary the air fuelratio so as to follow the change in the suitable ignition condition. Inthis case, however, such a problem has arisen as follows. That is,immediately after the ignition (t₂), as described above, the control ofthe turbine is switched from the phase of the driving by the motor toanother phase of the speed up control by the supply of the combustiongas. At that time, since the revolution speed of the turbine immediatelyafter the ignition (t2) is kept constant and the acceleration thereof isequal to zero, the acceleration of revolution of the turbine right afterthe switching of the control phase has a substantial deviation from thetarget acceleration thereof.

This makes the fuel flow control valve open to excessive degree rightafter the shifting to the speed up control phase due to a control actionneeded for minimizing this deviation. Therefore, the fuel is excessivelysupplied to the combustor through the fuel flow control valve, whichcause a problem that immediately after the ignition, the temperature ofthe gas turbine apparatus, in particular, of the combustor thereofrapidly rises up to high temperature (see the exhaust gas temperature ofFIG. 6). This problem occurs also in the case employing the startingmethod shown in FIG. 5.

FIG. 7 is a diagram of a revolution speed of the turbine, a temperatureof an exhaust gas, a quantity of fuel supply per unit time, and acurrent supply per unit time to a motor of an another conventional gasturbine apparatus during an igniting operation, each illustrated as afunction of an elapsed time. In FIG. 7, NR (Number of Revolution)represents a revolution speed of the turbine, FCV (Fuel Control Valve)represents an opening of the fuel flow control valve, EGT (Exhaust GasTemperature) represents a temperature of the exhaust gas, and MC (MotorCurrent) represents a quantity of current supply per unit time to themotor, respectively.

In this conventional gas turbine apparatus, first of all, the turbine isrotatively driven by the motor, and as shown in FIG. 7, after therevolution speed of the turbine reaches up to a certain revolution speedNR1 allowing for ignition, this revolution speed is maintained. Then,the fuel flow control valve is opened to start a fuel supply (t₁) to thecombustor, and the quantity of fuel supply per unit time is increasedgradually. In synchronism with the starting of the fuel supply, theigniting operation on the mixture of fuel and air produced in thecombustor is started, and when the air-fuel mixture is ignited (t₂), themixture is burned to generate the combustion gas.

After the air-fuel mixture is ignited and the combustion gas isgenerated, the combustion gas is fed to the turbine and thereby theturbine is rotatively driven by the combustion gas and the motor.Subsequently, the current supply to the motor is stopped (t₃), and afterthat, the turbine is rotatively driven only by the combustion gas fedthereto. Further, after the air-fuel mixture is ignited and thecombustion gas supply has been started (t₂˜), a speed up control isapplied in which the opening of the fuel flow control valve iscontrolled to increase the revolution of the turbine at a predeterminedtarget acceleration (ACCsp).

However, in this conventional gas turbine apparatus, like theconventional apparatus shown in FIGS. 5 and 6, immediately after thespeed up control has been applied (t₂), as shown in FIG. 7, the quantityof fuel supply per unit time is temporarily increased due to the speedup control to quickly raise the acceleration of revolution of theturbine from zero to the target acceleration (ACCsp) (see FCV in FIG.7). Accordingly, the exhaust gas temperature also rises up rapidly, andthereby the temperature of the gas turbine apparatus, in particular ofthe combustor thereof rises up quickly up to high temperature whichcould result in a serious damage thereof (see EGT of FIG. 7).

On the other hand, after the rotative driving for the turbine by themotor has been stopped, the turbine is required to increase therevolution speed only by the combustion gas fed thereto. This mightcause the additional problem that, right after the rotative driving bythe motor has been stopped (t₃), the quantity of fuel supply per unittime is increased by a control action to maintain the targetacceleration, which could result in a further temperature rise of thegas turbine apparatus.

SUMMARY OF THE INVENTION

The present invention has been made in the light of the problematiccircumstances described above and the object thereof is to provide a gasturbine apparatus and a starting method thereof, which improves areliability in starting operation by making it possible to ensure theignition of the air-fuel mixture under various conditions, and furthermakes it possible to depress the temperature rise of the gas turbine,which may otherwise occurs immediately after the ignition.

Another object of the present invention is to provide a gas turbineapparatus which makes it possible to depress the rapid temperature riseof the gas turbine apparatus during the igniting operation by preventinga rapid increase of the quantity of fuel supply provided for thecombustion.

In order to solve the problem described above, according to a firstaspect of the present invention, there is provided an innovativestarting method of a gas turbine apparatus comprising the steps ofrotatively driving a turbine by a motor coupled to the turbine, while atthe same time supplying a compressed air to a combustor by an aircompressor operating in interlocking motion with the turbine, starting afuel supply to the combustor when a revolution speed of the turbine hasreached up to a predetermined value, and simultaneously starting anigniting operation on an air-fuel mixture in the combustor, the methodcharacterized in that at least during the igniting operation to theair-fuel mixture in the combustor, a quantity of fuel supply per unittime to the combustor is increased while increasing the revolution speedof the turbine.

According to a second aspect of the present invention, there is providedan innovative gas turbine apparatus comprising a motor for rotativelydriving a turbine, a motor control section for controlling a revolutionspeed of the motor, a combustor for burning an air-fuel mixture therebygenerating a combustion gas therein, an air compressor for supplying acompressed air to said combustor, the compressor operating ininterlocking motion with the turbine, and a fuel flow control valve forcontrolling a quantity of fuel supply per unit time to the combustor,the apparatus characterized in that at least during the ignitingoperation to the air-fuel mixture in the combustor, a quantity of fuelsupply per unit time to the combustor is increased through the fuel flowcontrol valve while increasing the revolution speed of the turbine bysaid motor control section by the use of the motor.

According to the first and second aspect of the present invention, sincethe air fuel ratio can be controlled to follow the change in thesuitable ignition condition, it can be ensured to perform the ignitingoperation without any failure. Further, since the turbine has beenaccelerated to some extent when it is ignited, the deviation of theacceleration of revolution of the turbine at the point of ignition fromthe target acceleration thereof may be made small. Accordingly, anexcessive supply of the fuel immediately after the ignition followed bythe shifting to the speed up control phase can be avoided therebypreventing an excessive temperature rise in the gas turbine apparatus,which otherwise might occur right after the ignition.

According to a third aspect of the present invention, there is providedan innovative starting method of a gas turbine apparatus comprising thesteps of igniting a mixture of fuel and air while rotatively driving aturbine by a motor, to combust the mixture, and supplying a combustiongas generated by the combustion to the turbine thereby increasing arevolution speed of the turbine, the method characterized in that for apredetermined time period after the mixture has been ignited, a quantityof fuel supply per unit time provided for the combustion is held to beconstant.

According to the third aspect of the present invention, since thequantity of fuel supply per unit time is held constant for a certaintime period after the air-fuel mixture is ignited, an excessive fuelsupply can be prevented, which otherwise might occur immediately afterthe ignition. Consequently, the rapid temperature rise of the gasturbine apparatus could be prevented.

Further, according to a preferred embodiment of the third aspect, afterthe predetermined time period has elapsed, the quantity of fuel supplyper unit time is gradually increased while at the same time, therotative driving force for the turbine provided by the motor isdecreased gradually.

According to the third aspect of the present invention, after a rotativedriving mode of the turbine is gradually shifted from a driving phase bythe motor to a driving phase by the combustion gas, the rotative drivingof the turbine by the motor is stopped. As a result, since upon stoppingthe rotative driving by the motor, a control action for supplying theadditional fuel to maintain the target acceleration can be relaxed, anexcessive fuel supply may be depressed thereby preventing the rapidtemperature rise of the gas turbine apparatus.

Further, if the revolution speed of the turbine increases while holdingthe quantity of fuel supply per unit time to be constant after theignition, only the quantity of the air supplied into the combustorincreases, which results in a drop of the ratio of the fuel to the airin the mixture produced in the combustor. This could cause sometimes aspecific phenomenon referred to as a flame-out where a combustion flamegoes out. According to the preferred embodiment of the third aspect,since the quantity of fuel supply per unit time is once held constantand then increased gradually, the rapid temperature rise of the gasturbine apparatus can be avoided while preventing the flame-outphenomenon from occurring.

According to a fourth aspect of the present invention, there is providedan innovative gas turbine apparatus in which a mixture of air and fuelis combusted and a combustion gas generated by the combustion issupplied to a turbine to rotatively drive the turbine, the apparatuscharacterized in comprising an ignition means for performing an ignitingoperation on the air-fuel mixture while rotatively driving the turbineby a motor during starting operation, a fuel flow control valve ofvariable opening for controlling a quantity of fuel supply to beprovided for the combustion, an ignition detecting means for detectingan ignition of the air-fuel mixture; and an opening holding means forholding the opening of the fuel flow control valve to be constant for apredetermined time period after the ignition of the air-fuel mixture hasbeen detected by the ignition detecting means.

According to a preferred embodiment of the fourth aspect, the innovativegas turbine apparatus further comprises a driving force controllingmeans for gradually decreasing a current supply per unit time to themotor and at the same time gradually increasing the opening of the fuelflow control valve after the predetermined time period has elapsed.

In this case, it is preferable that the driving force controlling meanscomprises an air fuel ratio control section for controlling an air fuelratio of a mixture by operating the opening of the fuel flow controlvalve, and a current supply control section for controlling the currentsupply per unit time to the motor, wherein after the predetermined timeperiod has elapsed, the opening of said fuel flow control valve isgradually increased by the air fuel ratio control section whilecontrolling the motor by the current supply control section such thatthe turbine may keep a predetermined target acceleration of revolution.

Alternatively, it is also preferable that the driving force controllingmeans comprises a current supply control section for controlling thecurrent supply per unit time to the motor, and an acceleration controlsection for controlling an acceleration of revolution of the turbine byoperating the opening of the fuel flow control valve, wherein after thepredetermined time period has elapsed, the current supply per unit timeto the motor is gradually decreased by the current supply controlsection while controlling the turbine to keep the predetermined targetacceleration of revolution by the acceleration control section.

The above and other objects, features and advantages of the presentinvention will become more apparent from the following description whentaken in conjunction with the accompanying drawings in which preferredembodiments of the present invention are shown by way of illustrativeexamples.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram illustrating a general configuration of agas turbine apparatus according to an embodiment of the presentinvention;

FIG. 2 is a diagram of a revolution speed of a turbine, an opening of afuel flow control valve, and a temperature of an exhaust gas of a gasturbine apparatus during an igniting operation, each illustrated as afunction of an elapsed time, according to an embodiment of the presentinvention;

FIG. 3 is a schematic diagram illustrating a general configuration of agas turbine apparatus according to an another embodiment of the presentinvention;

FIG. 4 is a diagram of a revolution speed of a turbine, a quantity offuel supply per unit time, a temperature of an exhaust gas and a currentsupply per unit time to a motor of a gas turbine apparatus during anigniting operation, each illustrated as a function of an elapsed time,according to the another embodiment of the present invention;

FIG. 5 is a diagram of a revolution speed of a turbine, an opening of afuel flow control valve, and a temperature of an exhaust gas of aconventional gas turbine apparatus during an igniting operation thereof,each illustrated as a function of an elapsed time;

FIG. 6 is a diagram of a revolution speed of a turbine, an opening of afuel flow control valve, and a temperature of an exhaust gas of anotherconventional gas turbine apparatus during an igniting operation thereof,each illustrated as a function of an elapsed time; and

FIG. 7 is a diagram of a revolution speed of a turbine, a quantity offuel supply per unit time, a temperature of an exhaust gas and a currentsupply per unit time to a motor of a still further conventional gasturbine apparatus during an igniting operation thereof, each illustratedas a function of an elapsed time.

DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION

Preferred embodiments of the present invention will now be describedwith reference to the attached drawings.

FIG. 1 is a schematic diagram illustrating a general configuration of agas turbine apparatus according to an embodiment of the presentinvention.

As shown in FIG. 1, the gas turbine apparatus according to theembodiment of the present invention comprises a turbine 1, a combustor 2for supplying a combustion gas to the turbine 1, a fuel flow controlvalve 19 for controlling a quantity of fuel supply per unit time to thecombustor 2, an air compressor 3 for supplying a compressed air to thecombustor 2, and a turbine control section 11 for controlling theturbine 1.

The turbine 1 is equipped with a plurality of rotary vanes (not shown)for receiving a fluid for rotation, and rotatably supported via a rotaryshaft 6 in a casing (not shown). The air compressor 3 is driven by theturbine 1 via the rotary shaft 6 so as to compress the air. The aircompressor 3 is connected to the combustor 2 via a piping 7, so that theair compressed by the air compressor 3 is supplied to the combustor 2through the piping 7.

The fuel flow control valve 19 is disposed upstream to the combustor 2,and the fuel supplied from a fuel supply source, though not shown,passes through the fuel flow control valve 19 and then enters thecombustor 2. The fuel flow control valve 19 is configured to be of avariable opening type, such that the quantity of fuel supply to thecombustor 2 may be controlled by operating the opening thereof. It is tobe noted that the turbine control section 11 controls the turbine 1 byoperating the opening of the fuel flow control valve 19 so that anacceleration of revolution of the turbine 1 may approach to a targetacceleration.

The fuel and the compressed air supplied to the combustor 2 togetherproduce an air-fuel mixture in the combustor 2, where the air-fuelmixture is burned to generate a combustion gas of high temperature andhigh pressure. Then, the combustion gas is supplied to the gas turbine 1to revolve it at high revolution speed. A revolution speed detectingsection 12 for detecting a revolution speed of the turbine 1 isinstalled on the rotary shaft 6 at a position near to a terminal endthereof located in the motor 5 side.

The gas turbine apparatus according to this embodiment further comprisesthe motor 5 coupled to the rotary shaft 6 and a motor control section 8for controlling a revolution speed of the motor 5, as shown in FIG. 1.In this embodiment, the motor 5 functions as a starting motor for thegas turbine apparatus, wherein the motor control section 8 controls therevolution speed of the motor 5.

FIG. 2 is a diagram of the revolution speed of the turbine(NR), theopening of the fuel flow control valve(FCV), and a temperature of anexhaust gas(EGT) of the gas turbine apparatus of the present embodimentduring the igniting operation, each illustrated as a function of anelapsed time.

As shown in FIG. 2, when the gas turbine apparatus is to be started,first of all, an electric power is supplied to the motor 5 so that theturbine 1 may be rotatively driven by the motor 5 (see the dotted lineMC in FIG. 2). After the revolution speed of the turbine 1 has reachedup to a certain revolution speed suitable for ignition (NR,), the motor5 is controlled by the motor control section 8 such that the revolutionspeed of the turbine 1 may be increased gradually. At that time, sincethe motor 5 and the air compressor 3 are interlocked with each otherthrough the rotary shaft 6, the quantity of the compressed air supply tothe combustor 2 is also increased gradually.

Almost in synchronism with the starting of increase in the revolutionspeed of the turbine 1 by the motor control section 8, the fuel flowcontrol valve 19 is opened to start a fuel supply to the combustor 2(t₁). Further, upon starting the fuel supply to the combustor 2, thefuel flow control valve 19 is controlled to increase its openinggradually to increase the quantity of the fuel supply to the combustor2.

In the combustor 2, the mixture is produced by the compressed air andthe fuel, and the igniting operation on this air-fuel mixture is startedalmost in synchronism with the starting of the fuel supply to thecombustor 2. Although the air fuel ratio of the mixture suitable for theignition varies depending on conditions such as the temperature of thegas turbine main body, while during the igniting operation beingperformed (between t₁ and t₂), the actual air fuel ratio will vary sincethe quantities of the compressed air supply and the fuel supply to thecombustor 2 both increase as described above. Accordingly, the air-fuelmixture is ignited when the air fuel ratio reaches a certain valuematching the condition suitable for the ignition at that time.

After the igniting operation on the air-fuel mixture completed, thecombustion gas is supplied to the turbine 1, which obtains a drivingforce from the combustion gas to increase its revolution speed. Afterthe rotative driving of the turbine 1 by the combustion gas started(after t₂), the control mode is shifted to the speed up control phase bythe turbine control section 11. It is to be noted that whether or notthe igniting operation on the air-fuel mixture in the combustor 2 havingbeen completed is determined by measuring the exhaust gas temperaturewith an exhaust gas temperature measuring device 17 installed on thepiping.

Immediately after the control mode has been shifted to the speed upcontrol phase, since the turbine 1 has been accelerated by the motor 5to some extent as shown in FIG. 2, the deviation of the acceleration ofrevolution of the turbine 1 from the target acceleration thereof issmall at this point. Accordingly, as shown in FIG. 2, the fuel flowcontrol valve 19 is not required to open its opening excessively tobring the acceleration of revolution of the turbine 1 close to thetarget acceleration, and as a result, an excessive fuel supply to thecombustor 2 can be avoided thereby preventing an excessive temperaturerise in the gas turbine apparatus, which otherwise might occur rightafter the ignition.

FIG. 3 is a schematic diagram illustrating a general configuration ofthe gas turbine apparatus according to a second embodiment of thepresent invention.

As shown in FIG. 3, the gas turbine apparatus according to thisembodiment essentially comprises a turbine 1, a combustor 2 forcombusting a mixture of fuel and air, a fuel flow control valve 19 forcontrolling a quantity of fuel supply to the combustor 2, and an aircompressor 3 which operates in interlocking motion with the turbine 1for supplying a compressed air to the combustor 2, like theaforementioned embodiment.

The turbine 1 is equipped with a plurality of rotary vanes (not shown)for receiving a fluid for rotation, and rotatably supported via a rotaryshaft 6 in a casing(not shown). The air compressor 3 is driven by theturbine 1 via the rotary shaft 6 so as to compress the air. The aircompressor 3 is connected to the combustor 2 via a piping 7, so that theair compressed by the air compressor 3 is supplied to the combustor 2through the piping 7.

The fuel flow control valve 19 is disposed upstream to the combustor 2,and the fuel supplied from a fuel supply source, though not shown,passes through the fuel flow control valve 19 and enters the combustor2. The fuel flow control valve 19 is configured to be of a variableopening type, such that the quantity of fuel supply to the combustor 2may be controlled by operating the opening thereof.

The fuel and the air supplied to the combustor 2 together produce anair-fuel mixture in the combustor 2, where the air-fuel mixture isburned to generate a combustion gas of high temperature and highpressure. Then, the combustion gas is supplied to the gas turbine 1 torevolve it at high revolution speed. A revolution speed of the turbine 1is detected by a revolution speed detecting section 12 installed on therotary shaft 6 at a location near to a terminal end thereof, and therevolution speed of the turbine 1 detected by the revolution speeddetecting section 12 is sent to an acceleration control section 11′.

The acceleration control section 11′ calculates an acceleration ofrevolution of the turbine 1 by differentiating the revolution speed ofthe turbine 1 sent from the revolution speed detecting section 12, andcontrols the acceleration of revolution of the turbine 1 by operatingthe opening of the fuel flow control valve 19 so that the calculatedacceleration may approach a target acceleration.

A generator 5 is coupled with the rotary shaft 6 at a location near tothe terminal end thereof, through which the generator 5 is rotativelydriven by the turbine 1 to generate electricity. It is to be noted thatin this embodiment, the generator 5 is used as a starting motor duringthe starting operation. Accordingly, the generator will be sometimesreferred to as a motor in the following description.

The gas turbine apparatus according to this embodiment further comprisesan ignition means for performing an igniting operation on the air-fuelmixture while rotatively driving the turbine 1 by the motor 5 during thestarting operation, an ignition detecting means 22 for detecting theignition of the air-fuel mixture, an air fuel ratio control section 15for controlling a ratio between air and fuel in the air-fuel mixture byoperating the opening of the fuel flow control valve 19, a currentsupply control section 16 for controlling a current supply per unit timeto the motor 5.

In the present embodiment, the ignition means designates an ignitionplug (not shown) installed within the combustor 2. Further, the ignitiondetecting means 22 of the present embodiment comprises an exhaust gastemperature sensor 20 for measuring a temperature of the combustion gasafter having been supplied to the turbine 1, and an ignition determiningsection 21 for determining the ignition of the mixture when the exhaustgas temperature measured by the exhaust gas temperature sensor 20indicates a predetermined rising rate.

The air fuel ratio control section 15 is designed to hold the opening ofthe fuel flow control valve 19 to be constant for a predetermined timeperiod after the detection of the ignition of the air-fuel mixture bythe ignition detecting means 22. That is, the air fuel ratio controlsection 15 functions as a means for holding the opening (hereafterreferred to as an opening holding means). Further, the air fuel ratiocontrol section 15 is designed to gradually increase the opening of thefuel flow control valve 19 after the above predetermined time period haselapsed.

The current supply control section 16 makes it possible for the turbine1 to be controlled to a desired revolution speed and/or accelerationduring the starting operation by controlling the current supply per unittime to the motor 5. The current supply control section 16 is designedsuch that the turbine 1 may be held at a predetermined revolution speedsuitable for the ignition during the ignition means performing theigniting operation on the air-fuel mixture, and further designed suchthat the revolution of the turbine 1 may be increased at a predeterminedtarget acceleration while the quantity of fuel supply per unit time isheld constant by the air fuel ratio control section 15 after theignition of the air-fuel mixture.

According to the air fuel ratio control section 15 and the currentsupply control section 16 configured as described above, after thequantity of fuel supply per unit time has been held constant for thepredetermined time period following the ignition of the air-fuelmixture, since the quantity of fuel supply per unit time is graduallyincreased by the air fuel ratio control section 15, then a rotativedriving force of the turbine 1 by the combustion gas is increased. Atthat time, since the current supply control section 16 controls thecurrent supply per unit time to the motor 5 such that the revolution ofthe turbine 1 may increase at a target acceleration, the current supplyper unit time to the motor 5 is decreased in synchronism with theincrease of the rotative driving force provided by the combustion gas.

That is, when the acceleration of revolution of the turbine 1 is heldconstant via the motor 5, if the rotative driving force for the turbine1 provided by the combustion gas increases, in synchronism therewith,the rotative driving force for the turbine 1 provided by the motor 5decreases. Accordingly, in the present embodiment, the driving forcecontrol means is composed of the air fuel ratio control means 15 and thecurrent supply control section 16.

An operation of the opening holding means and the driving force controlmeans will now be described with reference to FIG. 4. FIG. 4 is adiagram of the revolution speed of the turbine, the quantity of fuelsupply per unit time, the exhaust gas temperature and the current supplyper unit time to the motor of the gas turbine apparatus of theembodiment shown in FIG. 3 during the igniting operation, eachillustrated as a function of the elapsed time. In FIG. 4, NR representsthe revolution speed of the turbine 1, FCV the opening of the fuel flowcontrol valve 19, EGT the exhaust gas temperature, and MC the currentsupply per unit time to the motor 5, respectively. As comparison, thosefor the conventional gas turbine apparatus shown in FIG.7 are shown bydotted lines.

As shown in FIG. 4, first of all, the turbine 1 is rotatively driven bythe motor 5, and when the revolution speed of the turbine 1 reaches upto a certain value NR1 suitable for the ignition, this revolution speedis maintained under a control of the current supply control section 16.Then the fuel flow control valve 19 is opened to start a fuel supply(t₁), and the fuel is supplied to the combustor 2 while graduallyincreasing a quantity of fuel supply per unit time. In synchronism withstarting of the fuel supply, the igniting operation is started by theignition means in the combustor 2.

When the air-fuel mixture is ignited (t₂), the air-fuel mixture iscombusted to generate the combustion gas, and consequently therevolution speed of the turbine 1 is increased since in addition to themotor, the combustion gas also provides a driving force to the turbine1. When the air-fuel mixture is ignited, the exhaust gas temperaturerises, and so the completion of the igniting operation to the air-fuelmixture is detected by the ignition detecting means 22.

When the ignition of the air-fuel mixture is detected by the ignitiondetecting means 22, for a predetermined time period starting from thisdetection time (from t₂ to t₃), the opening of the fuel flow controlvalve 19 is controlled to be constant by the air fuel ratio controlsection 15 and thereby the quantity of fuel supply per unit time to thecombustor 2 is kept constant (see FCV in FIG. 4). In prior art shown inFIG. 7, however, the acceleration control section 11′ applies a speed upcontrol mode right after the ignition and thereby the exhaust gastemperature rises up rapidly as shown by a dotted line in FIG. 4, but inthe present embodiment, the excessive temperature rise in the exhaustgas can be avoided since the quantity of fuel supply per unit timeprovided for the combustion by the air fuel ratio control section 15 isheld constant.

After the ignition of the air-fuel mixture ha been detected by theignition detecting section 22, the turbine 1 will receive the drivingforce from both of the combustion gas and the motor 5 to increase therevolution speed thereof. At that time, the current supply controlsection 16 controls the motor 5 such that the revolution of the turbine1 may increase with the predetermined target acceleration (ACCsp). Thisallows the revolution of the turbine 1 to increase with the targetacceleration (ACCsp) even while the opening of the fuel flow controlvalve is held constant.

After the opening of the fuel flow control valve 19 held constant forthe predetermined time period, then the air fuel ratio control section15 controls the fuel flow control valve 19 such that the opening thereofmay increase gradually with a predetermined increasing rate (t₃˜).Consequently, the rotative driving force for the turbine provided by themotor 5, or the current supply per unit time to the motor 5, isgradually decreased (see MC in FIG. 4) since the current supply controlsection 16 controls the revolution of the turbine 1 to be held at thepredetermined acceleration, as described above. That is, as the rotativedriving force by the combustion gas is increased by increasing theopening of the fuel flow control valve 19, the current supply per unittime to the motor 5 is automatically decreased to reduce the rotativedriving force by the motor 5.

When the current supply per unit time to the motor 5 is decreased andthe quantity of fuel supply per unit time provided for the combustion isincreased to some extent, the current supply to the motor is stoppedcompletely (t₄). Under this condition, the turbine 1 is required toincrease its revolution speed only by the combustion gas suppliedtherefor. After the current supply to the motor 5 has dropped to zero, amain controller for the apparatus is switched from the air fuel ratiocontrol section 15 to the acceleration control section 11′, whichapplies thereafter the speed up control to the turbine 1.

In this embodiment, the excessive supply of the fuel to the combustor 2,which otherwise might occur immediately after the current supply to themotor 5 having been stopped completely, can be avoided by graduallyshifting the driving mode of the turbine 1 from that by the motor 5 tothat by the combustion gas before stopping the current supply to themotor 5. Further, if the quantity of fuel supply per unit time providedfor the combustion is held constant while increasing the revolution ofthe turbine 1 after the ignition of the air-fuel mixture, the ratio ofthe fuel quantity to the air quantity in the mixture drops, which maysometimes lead to the flame out. In the present embodiment, however,since the quantity of fuel supply per unit time is once held constantafter the ignition and then increased gradually, the rapid temperaturerise of the gas turbine apparatus can be avoided while preventing theflame-out from occurring.

Next, a third embodiment of the present invention will be described.

General configuration of the gas turbine apparatus according to thethird embodiment is completely similar to that of the second embodiment.Further, in the present embodiment, the behaviors of the revolutionspeed of the turbine, the quantity of fuel supply per unit time, theexhaust gas temperature and the current supply per unit time to themotor of the gas turbine apparatus observed during the startingoperation are similar to those in the second embodiment. Therefore, theconfiguration and the action of the present embodiment accompanied withno specific descriptions therefor are similar to those of the secondembodiment, and the description thereof will be omitted.

The third embodiment is similar to the second embodiment in the pointthat the air fuel ratio control section 15 is provided as the openingholding means for the fuel flow control valve 19. A difference of thepresent embodiment from the second embodiment is that the former has adifferent driving force controlling means for gradually decreasing acurrent supply per unit time to the motor 5 while increasing thequantity of fuel supply per unit time. That is, in the presentembodiment, the driving force control means comprises the current supplycontrol section 16 and the acceleration control section 11′.

In the third embodiment, after the quantity of fuel supply per unit timeis held constant for a predetermined time period by the air fuel controlsection 15, the current supply per unit time to the motor 5 is graduallydecreased by the current supply control section 16 while holding therevolution of the turbine to be at a predetermined target accelerationby the acceleration control section 11′. When the current supply perunit time is decreased by the current supply control section 16, therotative driving force for the turbine 1 provided by the motor 5 isreduced. In response to this, the acceleration control section 11′controls the fuel flow control valve 19 to increase the opening thereofand thereby to increase the rotative driving force provided by thecombustion gas in order to keep the target acceleration of revolution ofthe turbine 1.

That is, under the condition where the acceleration of revolution of theturbine 1 is held constant by the acceleration control section 11′, ifthe current supply per unit time to the motor 5 is decreased, thequantity of fuel supply per unit time provided for the combustion isincreased by the acceleration control section 11′. As a result, thecurrent supply per unit time to the motor 5 and the opening of the fuelflow control valve 19 show the same behaviors with those of the secondembodiment described above.

Thus, though the present embodiment is different from the secondembodiment in the driving force controlling means, the behaviors of thequantity of fuel supply per unit time to the combustor 2 and the currentsupply per unit time to the motor 5 observed during the ignitingoperation are quite the same with those of the second embodiment.Therefore, the present embodiment, similar to the second embodiment, candepress the rapid temperature rise of the gas turbine apparatus whilepreventing the flame-out from occurring during the igniting operation.

It should be appreciated that the gas turbine apparatus of the presentinvention is not limited to those described in the above embodiments,but may be modified in various manners without departing from the spiritand the scope of the present invention.

As having been described above, according to the present invention,since the air fuel ratio can be controlled to follow the change in thesuitable ignition condition, it can be ensured to perform the ignitingoperation without any failure. Further, in the first embodiment, sincethe turbine has been accelerated to some extent when it is ignited, thedeviation of the acceleration of revolution of the turbine at the pointof ignition from the target acceleration thereof is small. Accordingly,an excessive supply of the fuel immediately after the ignition can beavoided thereby preventing an excessive temperature rise in the gasturbine apparatus, which otherwise might occur right after the ignition.

Also, in the second embodiment, by holding the quantity of fuel supplyper unit time constant for a certain period after the air-fuel mixtureis ignited, the excessive fuel supply can be prevented, which otherwisemight occur immediately after the ignition. Consequently, the rapidtemperature rise of the gas turbine apparatus could be prevented.

Further, by stopping the rotative driving of the turbine by the motorafter the rotative driving mode of the turbine is gradually shifted fromthe driving phase by the motor to the driving phase by the combustiongas, upon stopping the rotative driving by the motor, the control actionfor supplying the additional fuel to maintain the target accelerationcan be relaxed. Accordingly, the excessive fuel supply may be depressedthereby preventing the rapid temperature rise of the gas turbineapparatus.

Still further, by once holding the quantity of fuel supply per unit timeconstant and then increasing it gradually, the rapid temperature rise ofthe gas turbine apparatus can be avoided while preventing the flame-outfrom occurring.

1. A starting method of a gas turbine apparatus comprising the steps of:rotating a turbine by a motor coupled to said turbine, while supplying acompressed air to a combustor by an air compressor; starting a fuelsupply to said combustor when a rotation speed of said turbine hasreached a predetermined value, thus producing an air-fuel mixture; andstarting an igniting operation to ignite the air-fuel mixture in saidcombustor; wherein during the igniting operation prior to a time whenthe air-fuel mixture in said combustor begins to ignite, a quantity offuel supplied to said combustor per unit time is increased while therevolution speed of said turbine is increased.
 2. A gas turbineapparatus comprising: a motor for rotatively driving a turbine; a motorcontrol section for controlling a revolution speed of said motor; acombustor for burning an air-fuel mixture thereby generating acombustion gas therein; an air compressor for supplying a compressed airto said combustor, said compressor operating in interlocking motion withsaid turbine; and a fuel flow control valve for controlling a quantityof fuel supply per unit time to said combustor; wherein at least duringan igniting operation for the air-fuel mixture in said combustor, andprior to a time when the air-fuel mixture in said combustor begins toignite, a quantity of fuel supply per unit time to said combustor isincreased through said fuel flow control valve while increasing arevolution speed of said turbine by said motor through control of saidmotor control section.
 3. A starting method of a gas turbine apparatuscomprising the steps of: igniting a mixture of fuel and air whilerotatively driving a turbine by a motor, to combust said mixture; andsupplying a combustion gas generated by said combustion to said turbinethereby increasing a revolution speed of said turbine; wherein for apredetermined time period immediately after the mixture begins toignite, a quantity of fuel supply per unit time provided for thecombustion is held to be constant.
 4. A starting method of a gas turbineapparatus in accordance with claim 3, in which after said predeterminedtime period has elapsed, the quantity of fuel supply per unit time isgradually increased while at the same time, a rotative driving force forsaid turbine provided by said motor is decreased gradually.
 5. A gasturbine apparatus in which a mixture of air and fuel is combusted and acombustion gas generated by said combustion is supplied to a turbine torotatively drive said turbine, said apparatus comprising: an ignitionmeans for performing an igniting operation on the air-fuel mixture whilerotatively driving said turbine by a motor during starting operation; afuel flow control valve of variable opening for controlling a quantityof fuel supply per unit time to be provided for the combustion; anignition detecting means for detecting an ignition of the air-fuelmixture; and an opening holding means for holding the opening of saidfuel flow control valve to be constant for a predetermined time periodimmediately after the beginning of ignition of the air-fuel mixture hasbeen detected by said ignition detecting means.
 6. A gas turbineapparatus in accordance with claim 5, said apparatus further comprisinga driving force controlling means for gradually decreasing a currentsupply per unit time to said motor and at the same time graduallyincreasing the opening of said fuel flow control valve after saidpredetermined time period has elapsed.
 7. A gas turbine apparatus inaccordance with claim 6, in which said driving force controlling meanscomprises: an air fuel ratio control section for controlling an air fuelratio of a mixture by operating the opening of said fuel flow controlvalve; and a current supply control section for controlling the currentsupply per unit time to said motor; wherein after said predeterminedtime period has elapsed, the opening of said fuel flow control valve isgradually increased by said air fuel ratio control section whilecontrolling said motor by said current supply control section such thatsaid turbine may keep a predetermined target acceleration of revolution.8. A gas turbine apparatus in accordance with claim 6, in which saiddriving force controlling means comprises: a current supply controlsection for controlling the current supply per unit time to said motor;and an acceleration control section for controlling an acceleration ofrevolution of said turbine by operating the opening of said fuel flowcontrol valve; wherein after said predetermined time period has elapsed,the current supply per unit time to said motor is gradually decreased bysaid current supply control section while controlling said turbine tokeep the predetermined target acceleration of revolution by saidacceleration control section.